Drag racing is a very popular type of motor vehicle racing sanctioned by the National Hot Rod Association (NHRA) and several other organizations. Commonly two vehicles race at a time, each attempting to be the first to cross the finish line one quarter mile away. Starts are controlled by a pole, known as the "Christmas tree," which is disposed at the starting line between the two vehicles and which displays in a vertical arrangement a series of light pairs. From top to bottom there are several, typically three, yellow light pairs, followed by a green light pair and then a red light pair. The lights of each pair disposed to opposite sides of the pole such that each vehicle has a set of three yellow, one green and one red light which pertains to its start. The yellow lights alert the drivers that the race is about to start; the green lights signal that the drivers may release the vehicles; and a red light flashes if a driver fouls by releasing his vehicle prior to his green light.
Although drag racing involves competitions between vehicles which have been placed within a particular class due to factors such as engine size, a very popular form of drag racing, known as "ET" or "elapsed time" racing, has developed whereby cars of different classes race each other, the more powerful car being held for a longer time at the starting line. More specifically each drag racing vehicle does a number of individual time trail runs to establish a typical ET for the track. When two vehicles race, the track delays the display of the tree lights for the faster vehicle by an amount equal to the difference between the two vehicles' established ETs.
A common practice in drag racing is to run the engine up to a high engine speed, while simultaneously locking the car against forward motion. Locking is achieved by electronic apparatus which either causes the vehicles' brakes to be engaged or which causes reverse gear to be applied within the transmissions simultaneously with a forward gear, these latter devices being known as transmission brakes or trans brakes. The driver achieves a rapid start by causing the locking device to disengage at an appropriate time.
To maximize the likelihood of releasing the vehicle at the earliest possible moment, ideally at the same instant as the green light comes on, electrical apparatus known as delay boxes have been developed for controlling the release of the locking mechanisms. The driver selects a yellow light at which he displays the most consistent reflexes, then selects a delay time which represents the time from that light to green. The driver then releases the locking device control button at the optimum time for the driver, and the delay box then releases the vehicle after the selected time has elapsed. To date no such device has been developed which satisfactorily addresses what has become the most popular form of drag racing.